Ordered categorical responses

The SOCATT data set is used in the comparison of different software packages for multilevel modelling, conducted by
the Centre for Multilevel Modelling.
The SOCATT data consist of the responses to a set of dichotomous items on a woman's right to have an abortion.
The outcome variable (yij) is a score constructed from these items ranging from 1 to 7, with a higher score
corresponding to stronger support for abortion. Each of 264 respondents was asked the same set of questions on four occasions,
1983-1986, and yij denotes the response from individual i in year j